Due to the small number of atoms in nanostructures, additional charge is likely to cause significant changes in their structure and properties. Here, we examine the charge-dependent structural evolution of individual bucky-diamonds, which have been proposed as a promising candidate for biological and medical applications, using self-consistent charge density functional based tight-binding simulations. We find that there exists a threshold of excess charge for each model bucky-diamond, above which destruction of the structures ensues. Our results also reveal the existence of a phase transition between bucky-diamonds and onion-like carbon below the failure threshold.